This invention relates to parabolic solar concentrators and more particularly to the method of tracking same with the sun's rays as the sun moves through its solar day or trajectory ascribed more properly to the earth's rotation. Various types of amalgamations of collectors and concentrators have been patented, but generally fall into the basic catagories of collectors or concentrators. For the purposes of background we shall deal only with these basic types of solar collectors and solar concentrators.
The typical solar collector, as differing from a concentrator, may take various forms but often consists of what is called a flat plate collector with a number of methods of running a liquid, more often water, over the flat plate device attempting to transfer as much of the solar heat energy as is thermodynamically feasible into the liquid. The transfer liquid may be circulated within tubes or troughs taking a variety of configurations. These collectors typically do not provide the thermal efficiency of a solar concentrator in order to achieve the same BTU (British Thermal Unit) output that a solar concentrator developes. Such flat plate collectors require considerably more units and a much larger area space wise is consumed in order to accommodate the collector installation mounting. However, the advantage of the flat plate collectors lies within the fact that they essentially can be mounted relatively close to the mounting surface with relatively small protuberance above the mounting surface as compared to the solar concentrator. Furthermore, the flat plate collector does have the advantage of being passive in its ability to track the sun's trajectory on a solar day. That is, typically, the flat plate collector more often does not require complicated active opto-electro-mechanical tracking systems in order to focus the sun's rays onto its collecting surface.
Whereas the solar concentrator requires fewer units or less area installation space to achieve the equivelent thermal output efficiency as compared to a flat plate collector. Concentrators, however, generally necessitate some form of usually expensive tracking devices which often are opto-electro-mechanical in nature and hence may be subject to breakdowns as the nature of such devices often are. It is therefore stated that prior art devices in the realm of solar concentrators, because they focus the sun's rays on a narrow point or band in order to achieve higher thermal efficiency, have proven to be unsatisfactory from the standpoint that they require expensive and complicated tracking devices.
Prior art devices in the form of flat plate collectors lack the high thermal efficiency that concentrators do, but have the advantage of non-complicated non-moving automatic tracking of the sun. However, the tracking they do have is often arrived at with a compromise solar angle attempting to achieve the greatest efficiency during the mid-part of the day.
It is therefore an object of this invention to provide a non-active tracking concentrator that has the advantages of the passive tracking that a flat plate collector provides.
It is a further object of this invention to improve the concentrating capacity of a passive collector at all positions of the sun from sun up to sun down.
A further object of this invention is to provide an easily mounted concentrator capable of being retrofited to almost any normally used solar mounting surface such as a roof.
Another object of this invention is to provide a novel, easily manufactured concentrator structure which is efficient in use but also is low in initial cost and requires little or no maintenance.